A balance shaft generally includes a balancing portion which provides an eccentric weight to offset vibrations in the engine which are not inherently balanced. For example, a balance shaft may be used in a combustion engine to offset vibrations from a crankshaft, where the balance shaft and crankshaft are rotated in opposite directions to cancel out vibrations in the engine.
In some engine configurations, the balance shaft may be positioned such that during rotation it is at least partially submerged in the engine oil within an oil reservoir. The rotating balancing portion of the balance shaft may create significant turbulence in the engine oil by repeated contact between the external surfaces of the eccentric or balancing portion of the balance shaft and the oil in the reservoir, causing aeration of the oil, which may cause cavitation, reduce oil cooling capacity and oil life, and/or cause other effects which may be detrimental to engine performance.